Hydride Generation Research Articles

Structure Activity Relationships for Second‐Coordination Sphere Functional Group Dependent CO2 Reduction by Manganese Bipyridyl Electrocatalysts

AbstractA series of twelve second coordination sphere (SCS) functionalized manganese tricarbonyl bipyridyl complexes are investigated for their electrocatalytic CO2 reduction properties in acetonitrile. A qualitative and quantitative assessment of the SCS functional groups is discussed with respect to the catalysts’ thermodynamic and kinetic efficiencies, and their product selectivities. In probing a broad scope of functional groups, it is clear that only the aprotic ortho‐arylester SCS is capable of promoting the highly desired low‐overpotential proton‐transfer electron‐transfer (PT‐ET) pathway for selective CO production. The ortho‐phenolic analogues cause an increase in overpotential with a product selectivity favoring H2 evolution, consistent with a high‐overpotential pathway via the anionic [Mn−H]− intermediate. Alternative aprotic Lewis base functional groups such as trifluoromethyl, morpholine and acetamide are shown to also be capable of intermediate manganese hydride generation. The tertiary amine substituent, 2‐morpholinophenyl, exhibits a desirable product distribution characteristic of syn‐gas (CO : H2=30 : 48) with an impressive turnover frequency, while the secondary amine group, 2‐acetamidophenyl, induces a notable shift in selectivity with a faradaic yield of 55 % for the formate (HCO2−) product. In addition to their catalytic properties, cyclic voltammetry and infrared spectroelectrochemistry (IR‐SEC) studies are presented to probe pre‐catalyst electronic properties and the two‐electron reduction activation pathway.

A Portable Microplasma Optical Emission Spectrometric Device with Online Digestion Function for Field and Sensitive Determination of Lead in Biological Samples.

Accurate detection and screening of Pb in biological samples is helpful to assess the risk associated with lead pollution to human health. However, conventional atomic spectroscopic instruments are bulky and cumbersome, requiring additional sample pretreatment equipment, and difficult to perform field analysis with. Herein, a portable point discharge (PD) microplasma-optical emission spectrometric (OES) device with online digestion function is designed for field and sensitive determination of lead in biological samples. With rice as a model, online digestion of a batch of six 50 mg samples can be achieved in the HNO3 and H2O2 system within 25 min by a temperature control and timing module. Compared to the conventional microwave digestion, the digestion efficiency of this device reaches 97%. Pb in digestion solution is converted into volatile species by hydride generation (HG) and directly introduced into PD-OES for excitation and detection by a self-designed rotatable and telescopic cutoff gas sampling column. Six samples can be successively detected in 2 min, and argon consumption of the whole process is only <800 mL. Under the optimized conditions, the detection limit of Pb is 0.018 mg kg-1 (0.9 μg L-1) and precision is 3.6%. The accuracy and practicability of the present device are verified by measuring several certified reference materials and real biological samples. By virtue of small size (23.5 × 17 × 8.5 cm3), lightweight (2.5 kg), and low energy consumption (24.3 W), the present device provides a convenient tool for field analysis of toxic elements in biological samples.

Coprecipitation as a One-Step Se Separation for Determination of Isotope Ratios Completed with Revised Uncertainty Evaluation.

This study introduces a simplified purification method for analyzing 82Se/78Se isotope ratios in diverse natural samples using hydride generation MC-ICP-MS. Unlike the thiol resin method, which is time-consuming and sensitive to the concentrations of reagents used at individual stages, our proposed alternative is quicker, simpler, and robust. The procedure involves coprecipitation of selenium with iron hydroxide and dissolution in hydrochloric acid. Combining hydride generation and a second cleanup stage achieves sufficient purification for Se isotope ratio measurements. The method is efficient, taking 3-4 h after sample decomposition, utilizing common reagents [HCl, Fe(NO3)3, NH4Cl] without evaporation or clean lab conditions. Results on 82Se/78Se isotope ratios in various matrices are presented, comparing them with literature data. All isotopic results have been subjected to a newly proposed state-of-the-art approach to uncertainty estimation dedicated to isotope ratio measurements. The approach is based on applying Monte Carlo simulations with consideration of different samples' results normalized by the expected value. By doing that, we obtained estimated uncertainty for any Se sample with the influence of particular measurements on the final estimation included. We employ a Monte Carlo simulation-based uncertainty estimation approach for isotope ratio measurements, providing estimated uncertainty for each selenium sample.

A novel atmospheric pressure glow discharge system for sensitive determination of As, Sb, and Se by optical emission spectrometry following their hydride generation

Hydride generation (HG) was combined with an atmospheric pressure glow discharge (APGD), sustained in a completely novel system, to sensitively determine As, Sb, and Se by optical emission spectrometry (OES). The carrier gas with the analyte hydrides produced by chemical HG together with co-generated H2 was introduced into the APGD system, where atomization and excitation processes took place. It was revealed that the essential factors responsible for the high stability of the plasma were its operating with He discharge gas (instead of Ar), operating the gas nozzle (used to introduce carrier He) as a cathode, and forcing the cathode spot to cover most of the surface of the gas nozzle. Under optimized operating conditions, the measurement repeatability was 2–3%, proving the high stability of the HG-APGD system. The detection limits (DLs) of As, Sb, and Se were 0.6, 0.14, and 1.2 μg L−1, respectively, and compared to those previously reported for HG-APGD with liquid electrodes, the DLs were improved over 3 times. In addition to improved DLs, the novel system offered a simplified and more compact design. The accuracy of HG-APGD OES was verified using a recovery test and proved by high agreement between spiked and measured concentrations of As, Sb, and Se in mineral and tap water samples, reaching recoveries within the range of 96–103%.

Switchable hydrophilicity solvent-assisted solidified floating organic drop microextraction for separation and determination of arsenic in water and fish samples

The aim of the current study was to separate and determine arsenic in water and fish samples using a novel and green solidified floating organic drop microextraction (SFODME), which is based on switchable hydrophilicity solvent (SHS)-assisted procedure followed by hydride generation atomic absorption spectrometry (HG-AAS). The 4-((2-hydroxyquinoline-7-yl)diazenyl)-N-(4-methylisoxazol-3-yl)benzene sulfonamide (HDNMBA) and tertiary amine (4-(2-aminoethyl)-N,N-dimethylbenzylamine (AADMBA) were used as ligand and SHS, respectively. The use of SHS promotes quantitative extraction of arsenic complexes into an extraction solvent (1-undecanol). Some factors that impact extraction recovery were studied. Under optimal conditions, the limit of detection (LOD) and limit of quantification (LOQ) were 0.005 μg L−1 and 0.015 μg L−1, respectively. The calibration graph was linear up to 900.0 μg L−1 arsenic, with the enrichment factor is 267. The proposed SHS-SFODME methodology for arsenic quantification in water and fish samples was successfully implemented. The environmental friendliness and safety of proposed method were approved by the Analytical Greenness Calculator (AGREE) and the Blue Applicability Grade Index (BAGI) tools.

Pb2H2 +: convergent quantum mechanical study of seven lead hydride cation structures. Toward laboratory identification

ABSTRACT Lead is heavily utilised in industry, but it bears potential harm due to its toxic nature. Identifying lead is important in diagnosing and preventing lead poisoning. Hydride generation via inductively-coupled plasma mass spectrometer (HG-ICP-MS) can detect small amounts of lead with high accuracy. Here we investigate seven structures of Pb 2 H 2 + . The geometries of each structure were optimised using coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] method with the cc-pwCVQZ-PP basis set for lead and the cc-pVQZ basis set for hydrogen. Likewise, harmonic vibrational frequencies were obtained using the same method. Anharmonic frequencies were determined using CCSD(T) with cc-pwCVTZ-PP and cc-pVTZ basis sets for lead and hydrogen, respectively. The focal point approach (FPA), including CCSDT and CCSDT(Q) computations, was applied to the seven structures to find the relative energies with respect to the global minimum butterfly structure. Relative to the global minimum butterfly structure, the energies for the planar transition state, monobridged, vinylidene-like, trans, cis, and linear structures are: 1.1, 18.3, 26.5, 27.8, 28.8, and 93.7 kcal mol − 1 , respectively. Natural bond orders and dipole moments are reported as well. The predicted vibrational frequencies should be helpful in guiding the laboratory observation of Pb 2 H 2 + .

Synergistic Effects of Vitamin A and Spirulina on Arsenic Load in Rat Tissues and Blood

Arsenic (As) is found in contaminated groundwater as the source of pollution. In this study, 60 Long-Evans rats were used to assess the levels of As in the blood and organs and to compare the effectiveness of vitamin A and spirulina (Spirulina platensis) in preventing a chronic As accumulation. Twelve rats were assigned to each group of animals. The experimental groups were the control (T0), As (T1), As + spirulina (T2), As + vitamin A (T3), and As + spirulina + vitamin A (T4). The T1, T2, T3, and T4 groups were orally administered with sodium arsenite (NaAsO2) @ 4 mg/kg body weight (BW) for 63 days. In addition to NaAsO2, the T2 and T4 received 1 g/kg BW spirulina. The T3 and T4 received 2500 IU/kg BW vitamin A for 63 days, respectively. Four rats were euthanized in each group to evaluate the As concentration in the liver, lung, kidney, and blood at an interval of 21 days. Total As concentration was quantified from the organs using Hydride Generation Atomic Absorption Spectrophotometer (HG-AAS). The results revealed that the T0 had no visible clinical symptoms. However, after 63 days of treatment, the T1 (As only administration) accumulated more As compared to other groups. The concentration of As was highest in the blood, then in the kidney, liver, and lung. In this case, spirulina and vitamin A substantially (p&lt;0.01) decreased the concentration of As in the rats' organs and tissues Spirulina is more effective than vitamin A in reducing As accumulation in rats. In summary, the combination of both spirulina and vitamin A has a positive impact on reducing the accumulation of chronic arsenicosis in rats compared to the individual administration of either spirulina or vitamin A alone. Vol. 10, No. 3, December 2023: 341-351

Laser-Induced Breakdown Spectroscopy Applied to Elemental Analysis of Aqueous Solutions—A Comprehensive Review

Laser-induced breakdown spectroscopy (LIBS) has evolved considerably in recent years, particularly the application of portable devices for the elemental analysis of solids in the field. However, aqueous analysis using LIBS instruments, either in the laboratory or in the field, is rather rare, despite extensive research on the topic since 1984. Thus, our comprehensive review aims to provide a clear overview of this research to offer guidance to new users. To achieve this, we examined the literature published between 1984 and 2023, comparing various settings and parameters in a database. There are four different categories of LIBS instruments: laboratory-based, online, portable, and telescopic. Additionally, there are four main categories of sample preparation techniques: liquid bulk, liquid-to-solid conversion, liquid-to-aerosol conversion, and hydride generation. Various experimental setups are also in use, such as double-pulse. Moreover, different acquisition settings significantly influence the sensitivity and therefore the detection limits. Documentation of the different methods of sample preparation and experimental settings, along with their main advantages and disadvantages, can help new users make an informed choice for a particular desired application. In addition, the presentation of median detection limits per element in a periodic table of elements highlights possible research gaps and future research opportunities by showing which elements are rarely or not analysed and for which new approaches in sample preparation are required to lower the detection limits.

A robust method for the determination of lead in water samples using flow injection hydride generation atomic absorption spectrometry

Flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) is a sensitive technique for the quantification of trace amounts of lead. However, plumbane generation is not straightforward and usually HG methods for lead are not robust enough for routine analysis. The optimum pH range for Pb HG is very narrow, so strict control of the acidity of the reaction medium is required for reliable results and in some cases even acid concentrations used for sample preservation can interfere. Moreover, some elements, like Cu, can interfere in the HG reaction suppressing the Pb signal. In this paper we report the development and validation of a method for the determination of Pb in water samples that is robust towards acidity and Cu levels usually found in water samples.All hydride generation parameters were optimized, but special emphasis was put on robustness. The use of borate as a buffer significantly improved the robustness of the method towards acidity, compared to the typical non-buffered HG. Furthermore, the interference of Cu, Sb and Sn in the HG reaction was overcome using thiocyanate as a masking agent. Other elements do not interfere at levels typically found in water samples. The limit of quantification achieved (0.9 μg L−1) is below the current guideline value for Pb in drinking water (10 μg L−1). The linearity of the method was verified between the LOQ and up to 15 μg L−1. An analytical frequency of 25 samples per hour with 3 measurement replicates each was achieved. The method was applied to the analysis of 50 water samples. The concentrations found ranged from <LOD (0.3 μg L−1) and up to 88.8 μg L−1.The proposed method is robust, cost-effective, easily automated and does not require unconventional or expensive equipment. It can be applied for routine analysis of different types of water samples.

Theoretical insights into the generation and reactivity of hydride on the ZnO(101̄0) surface.

ZnO is an important catalytic material for CO/CO2 hydrogenation. In this work, the pristine ZnO(101̄0) and the surfaces with Zn-O dimer vacancies (ZnO(101̄0)-(Zn-O)DiV) and oxygen vacancies are calculated. We find that the hydride (H-) species can be generated via heterolytic H2 dissociation on these surfaces, and that ZnO(101̄0)-(Zn-O)DiV only needs to overcome the energy barrier of ∼0.10 eV. This is because the ZnO system has flexible orbitals for electron storage and release and the low-coordinated Zn3c atoms at the defect sites can form stable Zn-H- covalent bonds with high symmetry. Flexible Zn orbitals also impart the unique feature of activating multiple electrophilic adsorbates simultaneously as excess electrons exist. Moreover, we show that the covalent Zn-H- species can regulate the catalytic activity and selectivity for CO2 hydrogenation by preferentially producing *HCOO intermediates at Zn-O dimer vacancies. These results may help in the design of efficient Zn-based hydrogenation catalysts.

Final report for SIM.QM-S12: supplementary comparison for trace elements in natural water

Main textThe SIM Supplementary Comparison SIM.QM-S12 for Trace Elements in Natural Water was undertaken to assess and demonstrate the analytical capabilities of national metrology institutes (NMIs) and designated institutes (DIs) of SIM members (or other regions) for the accurate determination of trace elements in natural water at µg/kg levels.Evidence of successful participation in formal, relevant international comparisons is needed to document calibration and measurement capability claims (CMCs) made by NMIs and DIs.Seventeen NMIs and DIs participated. Participants were requested to evaluate the mass fractions, expressed in µg/kg, of arsenic, cadmium, lead and antimony in a natural mineral groundwater that was spiked with the respective elements. A variety of instrumental techniques including inductively coupled plasma mass spectrometry (ICP-MS), isotope dilution ICP-MS (ID-ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-OES), electrothermal atomic absorption spectrometry (ETAAS) and hydride generation flame atomic absorption spectrometry (HG-FAAS) were used by the participants for the determination.The NIST decision tree was used to assign the SCRV estimate for the proposed measurands and to calculate the degrees of equivalence of each national measurement standard following the IAWG Guidance on Using NIST Decision Tree for Comparison Reporting from 30 June 2023.Successful participation in SIM.QM-S12 demonstrates measurement for determination of elements in water matrices. Considering the IAWG Core Capability Matrix, this material falls into the matrix challenge called "Water/aqueous", which corresponds to the CCQM amount-of-substance category fresh water, and so will support CMCs for the metalloids and semi-metals at mass fraction levels below 50 µg/kg (As and Sb measurements) and transition elements at mass fraction levels below 50 µg/kg (except Hg) (for Cd and Pb measurements).To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Design and construction of pilot sludge drying package for the excess sludge in petrochemical industries: Heavy metals determination in sludge by polarography and atomic absorption spectrometry

In this research, according to the high amount of sludge in a petrochemical company, an iron package type of drying sludge bed was made/designed with carbon steel. Then, the drying sludge pond was filled with layers of sand with different mesh sizes. The excess sludge from the sedimentation pond was passed over this bed, and the amount of sludge removed by the bed was obtained at %96. The values of heavy metal and microbial forms were determined using the proposed method based on activated sludge after wastewater treatment. For the validation process, 10 mL of deionized water (DW) was mixed with 1.0 g of dried sludge with pure nitric acid (2% HNO3), and then the solid phase was filtered with the Whatman filter (WF). The concentration of heavy metals (As, Cd, Cu, Pb, Hg, Mo, Ni, Co, Se, Zn) in the remaining solution of sludge (mg kg-1) and wastewater (µg L-1) was extracted/ separated based on sulfur-doped graphene oxide adsorbent (SDGO) by solid-phase microextraction procedure (SPME) before being determined by the flame and hydride generation atomic absorption spectrometry (F-AAS; HG-AAS) which had similar range to the polarography analysis. The LOD, linear range and preconcentration factor (PF) for metals were obtained.

Highly sensitive analysis of trace germanium derived from the efficient electrosynthesis and spectral introduction of GeH4 on foam electrode

BackgroundThe electrochemical hydride generation technology, which uses electrolysis instead of chemical reagents to generate reducing species to achieve gaseous transformation and sample introduction of the tested elements, has received widespread attention in the field of atomic spectroscopy due to its simple, economical, and green characteristics. However, limited by the effective area of the electrode, the introduction efficiency and spectral signal of most elements (e.g., germanium) in practical applications are lower than traditional chemical hydride generation. ResultsIn this paper, an efficient electrochemical hydride generation (EHG) method based on metal foam electrode for μg L−1 level germanium was constructed. Systematic electrochemical and spectral tests showed that the low charge transfer resistance and the high electrochemical activity of nickel-based foam electrodes jointly promoted the efficient electroreduction of Ge(IV). Besides, the porous network structure of the metal foam material improves the contact probability of reactants while reducing the gas-evolution effect caused by bubble accumulation. Interestingly, adequate reaction sites are crucial for the conversion of germanium, but large foam electrodes are not always compatible with analytical performance. After coupling atomic fluorescence spectroscopy, this new electrolysis method has been proven to be suitable for efficient conversion and quantitative detection of Ge over a wide concentration range (5–150 μg L−1). SignificanceOur proposal to improve the electrosynthesis efficiency of germanane (GeH4) by using metal foam electrode is extremely effective for the detection of trace or ultra-trace germanium. The exploration of electrode material, structure, and especially effective area will also provide ideas for the establishment of highly sensitive analysis methods in the future.

Metals bioaccumulation in fish captured from Araguari River upper section (Amazon biome), and risk assessment to human health resulting from their consumption

BackgroundThe Araguari River is one of the most important rivers from Amapá State and its waters are essential as source of drinking water and food, especially for the traditional Amazonian populations. These populations have fish as their main protein source; however, studies have shown the metals bioaccumulation in fish caught in the Araguari River and the risks to human health resulting from fish consumption. Our objective was to investigate the bioaccumulation of Cd, Pb, Cr, Ni, Fe, Mn, Cu, Zn, and Hg in muscle tissue from the fish species Ageneiosus inermis and Hoplias aimara, and to evaluate the risks to human health resulting from their consumption. MethodsFish sampling was carried out between September and October 2018 at two sampling sites located in the Araguari River upper section. The metal concentrations quantification was performed by Atomic Absorption Spectrometry, except for Hg whose concentrations were determined using a hydride generator coupled to Inductively Coupled Plasma Optical Emission Spectrometry. For risk assessment of each metal individually we use the risk quotient (RQ) approach. To assess the risk of metal mixtures, present in fish muscle samples, we used the risk index (RI) approach. We also calculate the estimated daily intake (EDI). ResultsThere was no statistical difference in the bioaccumulation of metals between both fish species. Only Cd and Pb presented average concentrations higher than the maximum limits established by Brazilian legislation aimed at protecting human health. The RI values obtained for both fish species were > 25, which indicates high risks to human health. The EDI values obtained for Hg in both fish species exceeded their reference dose (RfD). Taken together, our results show that these fish species are unfit for consumption. ConclusionsBased on our results we recommend that the population does not consume the species A. inermis and H. aimara. When suspending consumption of both species is not possible, reducing their consumption is mandatory to reduce the exposure of human populations to toxic metals bioaccumulated in fish muscle tissue and thus reduce health risks.

Ag-containing metal organic framework reacted with AsH3: Mechanism and application for inorganic arsenic detection by hydride generation-smartphone RGB readout colorimetric system.

The reaction mechanism of Ag-containing metal organic framework (Ag-BTC) and hydrogen arsenide (AsH3) was discussed in detail in this work. Silver ions in Ag-BTC were reacted with AsH3, and silver nanoparticles were generated on the surface of Ag-BTC, causing its color changed. This property was further applied to a hydride generation-colorimetric analytical system. As(III) was converted to AsH3via hydride generation and then reacted with the Ag-BTC (immobilized on test paper), leading to the test paper changed from white to black. Visual colorimetric and smartphone RGB readout mode were used for this analytical system. The results could be readout by naked-eye in visual colorimetric mode and a smartphone in RGB readout mode. Under the optimized conditions, As(III) concentration as low as 10μg/L and 50μg/L could be readout by smartphone and naked-eye, respectively. This method was further successful applied to As(III) determination in real samples (drinking water samples and scented tea samples), with recoveries of 91-113%.

Migration of antimony from polyethylene terephthalate bottles to mineral water: Comparison between test conditions proposed by Brazil and the European Union

This work evaluated the Sb content in polyethylene terephthalate (PET) bottles of mineral water, as well as the migration of Sb, according to the conditions established by Brazilian and European Union (EU) legislation. The total Sb content in the PET bottles was determined by the mineralization of the packaging followed by quantification by inductively coupled plasma optical emission spectrometry (ICP-OES). The migration of Sb from the bottle to the mineral water was carried out after the contact conditions established by Brazilian and EU legislation (40 °C for 10 days and 60 °C for 10 days, respectively). The migrated Sb content was determined directly in the solution, after pre-reduction with L-cysteine, using an ICP-OES coupled with a hydride generator. All evaluated packages showed Sb levels ranging from 173 mg kg−1 to 253 mg kg−1. The migration of Sb to the mineral water after 10 days at 40 ºC in contact with PET bottles was lower than the limit of quantification and after contact at 60 ºC for 10 days it was between 1.59 and 4.42 µg L−1. The highest contact temperature established by the EU favored Sb migration. However, all Sb migration results are within the limits established by Brazilian and EU legislation.

A simple and rapid copper-assisted microprecipitation method for the on-site separation of inorganic arsenic species in water samples followed by hydride generation atomic fluorescence spectrometry determination

A simple and rapid microprecipitation procedure was developed using copper (Cu2+) as precipitating agent for the separation–preconcentration of inorganic arsenic species (As(III) and As(V)) in waters prior to their determination by hydride generation atomic fluorescence spectrometry (HG-AFS). This procedure is based on selective precipitation of anionic species of As(V) with Cu2+, leaving neutral As(III) in the filtrate. The complexation of As(V) with Cu(II) entails the precipitation as copper arsenate, Cu3(AsO4)2 due to its low solubility product. The copper arsenate precipitate was characterized by XRD and EDS measurements. Optimum conditions for efficient microprecipitation process are; pH: 5 to 6, Cu/As mass ratio: 100, equilibration time: 2–3 min and eluent volume: 2 mL of 0.03 mol L−1 HCl. A fast process time of 2 min is enough for the on-site separation of As(III) and As(V) with the detection limits (LOD) 0.012 and 0.034 μg L−1 respectively. The recoveries were found to be in the range of 98–102%. This simple and fast method was successfully utilized for the on-site separation of As(III) and As(V) in wide variety of water samples collected in and around Kiradalli Tanda village, Karnataka state, India, where severe arsenic-contamination exists in various water bodies.

Mechanisms of chemical vapor generation by aqueous boranes for trace element analysis: a rather long and unfinished story

Abstract This paper reports a summary of the studies on the mechanisms that govern the generation of hydrides and other volatile species through reaction with aqueous boranes (CVG). This derivatization reaction has been used since the early 1970s for elemental determination and speciation from the trace level down to the ultratrace level and below. An IUPAC project, concluded in 2011, reported on the mechanisms of hydrogen transfer from borane to the analytical substrate and served to remove erroneous concepts that had dominated CVG until the early 2000s. Following the conclusion of the IUPAC project, many studies have been published on the mechanisms of CVG under conditions approaching those of analyzes of real samples. These studies included the definition of more general reaction models, which valid under non-analytical conditions, the mechanism of action of additives and interferences in CVG of volatile hydrides. In addition to the analytical utility for CVG, the results represent a contribution to the knowledge of the chemistry of aqueous boranes. Other studies will be necessary to clarify still unknown aspects, among them the identity of volatile transition metal species formed by reaction of metal ions with aqueous boranes.

PAN-templated synthesis of layered Co3O4 nanosheets for rapid reduction of 4-NP to 4-AP: Improved formation of unique Co3+-rich (440) facet on the crystal lattice of Co3O4

The efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using Co3O4 in NaBH4(aq) requires the precise control of hydride (Hδ-) and protic hydrogen (Hδ+) generation. Currently, this is achieved using (311) facet-dominated Co3O4 with Co2+-rich edges that favor Hδ- activation leading to poor performance. Herein, we employ the ladder-like structure of oxidized polyacrylonitrile (PAN) to fine-tune the growth of the (311)-to-(440) facets in layered Co3O4 nanosheets. This yields a balanced distribution of Co3+/Co2+ edge sites, leading to enhanced catalytic activity. Our catalyst is prepared by air-annealing a mixture of cobalt acetate (Co(OAc)2) and PAN at 500 °C. The mass ratio of Co(OAc)2 to PAN dictates the (311)/(440) facet ratio (i.e., Y). Specifically, a ratio of 0.25/0.4 (P-0.25–500) gives Y= 1.12. Meanwhile, at ratios of 0.05/0.4 (P-0.05–500) and 0.5/0.8 (P-0.5–500), Y increases to 1.25 and 1.27, respectively. XPS analysis confirms that the surface Co3+/Co2+ distribution (X) on P-0.25–50, P-0.05–500, and P-0.5–500 is 0.43, 0.41, and 0.39, respectively, highlighting a direct relationship between the (440) exposure and Co3+ concentration. The rate of 4-NP reduction (i.e., kapp) on P-0.25–500, i.e., ∼2.84 × 10−2 s−1 is 3.1x and 3.6x faster than P-0.05–500 (∼9.16 ×10−3 s−1) and P-0.5–500 (∼7.81 ×10−3 s−1), respectively. P-0.25–50's performance is comparable to that of state-of-the-art noble metal catalysts and higher than commercial Co3O4, and it maintains a decent catalytic retention of 88.84% after six recycles, demonstrating high stability. Our research presents a simple yet highly effective method for achieving balanced Hδ+ and Hδ- activation edges in Co3O4, resulting in superior 4-NP reduction activity.

The effect of selenium co-ingestion on mercury bioaccessibility in contaminated fish of the Amazon region

Mercury (Hg) is a toxic element that contaminates humans by consuming fish with high concentrations due to biomagnification in the food chain. This situation primarily impacts the riverside population in the Amazon region, as fish is their staple food. The interaction between selenium (Se) and Hg is well known due to their respective conceptual Pearson (soft-soft) characteristics. However, there needs to be more understanding of the impact of Se co-ingestion on Hg bioaccessibility. This scenario has prompted the investigation into the effects of consuming Se-rich food on the potential bioaccessibility of Hg when simultaneously ingesting contaminated fish. Cold vapor atomic absorption spectrometry (CV-AAS) measured Hg, and a hydride generator (HG-AAS) was used for Se. The results indicated that the piscivorous species Cichla sp. (Tucunaré fish) exhibited a Hg concentration over twice the limit established by the European Commission: 2.94 ± 0.21 μg g−1 for raw fish and 2.64 ± 0.16 μg g−1 for cooked fish. Concomitant ingestion of beans can reduce the potential bioaccessibility of Hg by 42% (68.4 to 25.8), and Brazil nuts co-ingestion can be reduced by 45% (68.4 to 23.1). However, due to the high fish consumption in the riverside population's diet, the Hazard Index (HI) and Target Hazard Quotient (THQ) values, including beans and Brazil nuts, exceeded the safe limit, even though THQ had decreased by 55%, and 66% with adding beans and Brazil nuts, respectively. These findings underscore the significant potential of Se in reducing Hg bioaccessibility through co-ingestion of foods containing this element. Additionally, it highlights the importance of considering regional dietary habits when assessing potential health risks. The results also sound like a warning about the food safety of the local communities.